WiMAX, or WiMAX-I, is based on the IEEE (Institute of Electrical and Electronics Engineers) 802.16e standard. WiMAX-I employs orthogonal frequency division multiple access (OFDMA) for transmissions, resulting in improved multi-path performance in non-line-of-sight environments. WiMAX-I may employ single-user (SU) or multiple-user (MU) multiple-input multiple output (MIMO) antenna techniques, adaptive modulation and coding schemes, and flexible subchannelization. A new generation of WiMAX termed 802.16m is currently under development.
Under fixed WiMAX, a limited form of subchannelization is supported in the uplink only. Mobile WiMAX permits subchannelization in both the uplink and the downlink. Currently, there exist multiple subchannelization schemes for dividing frequency/time resources between users. Partially used sub-channel (PUSC), fully used sub-channel (FUSC), and adaptive modulation and coding (AMC) are three subchannelization schemes that may be used for mobile WiMAX.
An OFDMA symbol is made up of sub-carriers, divided into data sub-carriers, pilot sub-carriers, and null sub-carriers (e.g., guard band). Subchannelization schemes divide the available sub-carriers into groups called logical resource units (LRUs). The LRUs may include contiguous sub-carriers (localized) or sub-carriers that are more random in their distribution (distributed).